This application claims the priority of German patent document 101 01 990.4, filed Jan. 18, 2001, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method for detecting wires using a synthetic aperture radar system based upon rotating antennas (ROSAR).
One of the greatest dangers in helicopter flight is that the pilot might overlook a wire obstacle located across his flight path, which could result in a serious accident or crash. This risk is increased under adverse weather conditions, such as rain, fog, snowfall, etc. The systems currently provided on board a helicopter are purely passive systems, such as residual light amplifiers, heat imaging systems, etc., which cannot be used under conditions of fog, smoke, and precipitation, due to their limited range. And recently implemented optical, electro-optical, and laser-based imaging systems also cannot significantly improve the situation in terms of detecting wire obstacles under adverse weather conditions, fog, or smoke.
German patent documents DE 39 22 086 and DE 43 23 511 disclose a ROSAR system that operates on-line in near real time, and can be used not only in mapping and mine detection applications, but also for detecting obstacles. The provided detection of wires via reflection points in various resolution cells, however, assumes a strong dominance of the reflection of the wire cross sections within a resolution cell. If this prerequisite is not met, costly postprocessing of the ROSAR images may improve the detectability of wires; however this method is not only costlyxe2x80x94as mentioned abovexe2x80x94it also cannot be considered sufficiently accurate.
One object of the present invention is to provide a method which guarantees optimized wire detectability based upon a ROSAR focusing system.
This and other objects and advantages are achieved by the detection method according to the invention, which is based on ROSAR focusing of entire segments of wire. By generating a wire reference signal comprised of a sum of coherent reference signals, reliable wire detectability is provided.
As shown in FIG. 5, ROSAR rings are generated by a rotating receiving antenna located on the tip of a rotor blade. The rotating receiving antenna itself describes a circle with a radius being the length of the rotor blade (not illustrated). The wire, which is disposed at a distance R0 from the position of the helicopter, extends over several adjacent range rings. When a helicopter approaches a wire obstacle, the approach of the wire obstacle to that circle is necessarily always tangential, independent of the position of the helicopter and the position of wire obstacle. The continued approach is then always parallel to this. Thus, the number of possibilities for approaching is reduced. For further calculation it is assumed that the wire obstacle is a straight wire segment. This assumption is sufficiently accurate because a wire drawn between two sustainers is approximately straight. Consequently, for determining the wire reference signal a straight wire segment is assumed.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.